How do I properly use an alpha texture to create variable transparency areas on a surface?
I have a solution of sorts. Here is my final node array:

That's just Texture mode (to illustrate how the alpha is figured out).
For a quick and dirty solution, this is just fine. I even went ahead and omitted the alpha map and just drove that value via the diffuse map.
If someone has a superior node-array in mind, I'm sure happy to listen though.
Here's a final render: